1. Field of the Invention
The present invention relates to a drive system for an automotive vehicle of the front-and-rear wheel drive type.
2. Description of the Prior Art
As one of drive systems for an automotive vehicle of the front-and-rear wheel drive type, there has been proposed a drive system composed of a primary drive mechanism for a set of primary road wheels and an ancillary drive mechanism for a set of ancillary road wheels. In the drive system, the primary drive mechanism is operated to drive the primary road wheels during usual traveling of the vehicle, and the ancillary drive mechanism is operated with the primary drive mechanism to drive the primary and ancillary road wheels at start of the vehicle and during low speed traveling of the vehicle. A drive system of this type is disclosed in Japanese Patent Laid-open Publication No. 2001-253256.
In the drive system, the primary drive mechanism is placed at a front wheel side of the vehicle to be driven by a prime mover of the vehicle, while the ancillary drive mechanism is placed at a rear wheel side of the vehicle to be driven by an electric motor. The drive system includes a first generator driven by the prime mover of the vehicle, a low voltage battery charged with an electric power supplied from the generator, a second generator driven by the prime mover of the vehicle, and an electric motor supplied with an electric power from the second generator for drive of the rear road wheels of the vehicle.
In the drive system, it is advantageous that a longitudinal drive shaft indispensable for transmitting the drive power of a prime mover to a set of rear road wheels in a conventional automotive vehicle of the four-wheel drive type is not required. This is significantly useful to reduce the vehicle weight for decrease of energy consumption.
In the drive system of this type, however, driving conditions of front and rear road wheels and change-speed conditions of the primary drive mechanism such as the prime mover and the power transmission of the vehicle are independently controlled since the front and rear road wheels are not mechanically interconnected by a conventional propeller shaft. Accordingly, if the drive power to the road wheels becomes excessive in a condition where the road wheels are driven by the primary drive mechanism on a road surface of low μ, there will occur racing of the road wheels, resulting in deterioration of the traction performance of the vehicle.